Hi Barry,
Thanks for your reply. I do have to clarify something though.
The sealant that I used is CS3204 a fuel resistant sealant for use on
integral fuel tanks and pressurized cabins as well as other areas subject
to contact with aircraft fuels, lubricants, oils, water and/or weathering. At
room temperature, this two-part polysulfide cures to a flexible, resilient
rubber.
Meets requirements of specifications AMS-S-8802 formerly MIL-S-8802,
CMNP021, Lockheed, Gulfstream, Hughes Aircraft, Fairchild SPS 6-1 & 6-2
​.

This is the same sealant that has been used on over 500 Van's RV-12's as
well as most other Van's aircraft (about 10,000 of them over the years).
The prototype RV-12 is over 5 years old and has flown most of it's time
with auto-gas. No problems so far. The new tank that I built also used that
same sealant.​ I still do not know why the original fuel tank that I built
failed after being in service for three years. I am not aware of any other
similar failures.
Clearly, not all sealants are the same.
Henry

Today's complete RotaxEngines-List Digest can also be found in either of
the
two Web Links listed below. The .html file includes the Digest formatted
in HTML for viewing with a web browser and features Hyperlinked Indexes
and Message Navigation. The .txt file includes the plain ASCII version
of the RotaxEngines-List Digest and can be viewed with a generic text
editor
such as Notepad or with a web browser.

I have a fuel problem that I would like your advice on. I have an RV-12
with the Rotax 912ULS that only has about 75 hours on it over the last
three or four years. I had some severe medical problems and my RV also had
some fuel problems. The fuel problems began with leakage from the tank. I
built the tank as per Van's manual and it sat for about a year before I put
any fuel into it. It was then OK for well over two years before there was a
leak. It began as a minor leakage and I removed the tank and sealed, from
the outside, one seam and a front corner. That did not stop the leak and it
got worse to the point that the tank lost about three gallons of auto fuel
over about four days. I removed the tank and could not find any sign of a
leak with the tank on the bench even with fuel in the tank. I put the tank
back in and filled it, again with auto fuel. It was OK for about five days
and then began to leak again, this time it lost about ~five gallons and
stripped the paint off the bottom of the plane, a real mess. I took a sheet
of newspaper and slid it under the tank, before I removed the fuel, and
found that it was leaking at the rear right corner. When I took the tank
out that time it did not leak on the bench until it had sat there for over
a week. The Pro-Seal softened up in places when it was wet with fuel but it
was OK when it dried out. While it was wet I could poke a Q-tip stick
through the corner, the Pro-Seal was quite soft. had no ideas why the
Pro-Seal broke down as it did but rather than risk another leak in flight I
made a new tank, this time without the side gauge and with a Moler
mechanical gauge on the top. There was a lot of trouble starting the engine
and when it did start, with full choke and no throttle, it ran rough. I had
to run the engine on full choke for at least five minutes before I could
even crack the throttle open. I cleaned both carbs and tried again. Before
the five minutes were up if I tried to open the throttle the engine would
die. Once it had really warmed up it seemed OK. I did the pre-flight check
with a run up at 4000 rpm. The ignition drop as less than 250 rpm and both
ignitions were the same. At full throttle I could not get more than 4400
rpm and it ran rough again. Back at the hangar I tried a few diagnostic
things. With the electric fuel pump on I see about 2.5-2.9 psi. With the
engine running and the electric pump off the fuel pressure drops to~0.5
psi. I took the fuel pump off the engine and operated it by hand, it seems
OK but needs the electric pump on to keep it primed. The throw of the pump
plunger is ~3/8"-7/16". Checking the pump cam with a rod and measuring the
amount of difference from high cam to low cam it is barely 3/16" which
seems very little. There is no sign of wear on the cam when looking at it
through the pump mounting hole. I had thought that the pump filter was
contaminated but the pump, when off the engine, seems OK.
The questions:
1) Is this a normal throw for this cam?
2) Why does it need so much choke when it did not do so before all the fuel
problems.
3) Is there something else I am missing that would cause these symptoms?
Since pulling off the fuel pump off another mechanic remarked that the
engine seemed very stiff to pull over with the prop, it had always been
that way since new and I had attributed it to the engine gearbox
combination. I removed the top plugs and the gearbox and the engine and the
gearbox are each quite smooth but not when the gearbox is mounted back on
the engine. It feels like the plugs are still in and there is compression
pressure causing resistance?
I apologize for the long description.
Henry

I have been working with gas tank sealants for over 20 years. I do not
know what form of PRO SEAL you used, what type did you use, the 890 or the
1440? But, I can tell you that ALL the gas tank sealants available in the
USA will NOT work with AutoGas (MoGas) that contains ethanol. The gas will
soften and cause leaks to the sealant. They are good, not great, with
MoGas that does NOT contain ethanol. YET! The 'Aromatics' in gas will
also attack tank sealants. Just not as fast as ethanol!
Also - Many, Many people put one layer of tank sealant over the top of the
old sealant... Ya CAN'T do that! The sealants DO NOT stick to them selves
once cured and especially after gas has been in the tank. You MUST remove
all the old sealant - Get down to bare metal - And start again.

As for your rotax running rough... Don't know... Maybe a broken part of
the sealant has blocked some orifice. I would fix one problem at a time.
Gas tank sure sounds like it should be first.

> I have a fuel problem that I would like your advice on. I have an RV-12
> with the Rotax 912ULS that only has about 75 hours on it over the last
> three or four years. I had some severe medical problems and my RV also
had
> some fuel problems. The fuel problems began with leakage from the tank. I
> built the tank as per Van's manual and it sat for about a year before I
put
> any fuel into it. It was then OK for well over two years before there
was a
> leak. It began as a minor leakage and I removed the tank and sealed, from
> the outside, one seam and a front corner. That did not stop the leak and
it
> got worse to the point that the tank lost about three gallons of auto
fuel
> over about four days. I removed the tank and could not find any sign of a
> leak with the tank on the bench even with fuel in the tank. I put the
tank
> back in and filled it, again with auto fuel. It was OK for about five
days
> and then began to leak again, this time it lost about ~five gallons and
> stripped the paint off the bottom of the plane, a real mess. I took a
sheet
> of newspaper and slid it under the tank, before I removed the fuel, and
> found that it was leaking at the rear right corner. When I took the tank
> out that time it did not leak on the bench until it had sat there for
over
> a week. The Pro-Seal softened up in places when it was wet with fuel but
it
> was OK when it dried out. While it was wet I could poke a Q-tip stick
> through the corner, the Pro-Seal was quite soft. had no ideas why the
> Pro-Seal broke down as it did but rather than risk another leak in
flight I
> made a new tank, this time without the side gauge and with a Moler
> mechanical gauge on the top. There was a lot of trouble starting the
engine
> and when it did start, with full choke and no throttle, it ran rough. I
had
> to run the engine on full choke for at least five minutes before I could
> even crack the throttle open. I cleaned both carbs and tried again.
Before
> the five minutes were up if I tried to open the throttle the engine would
> die. Once it had really warmed up it seemed OK. I did the pre-flight
check
> with a run up at 4000 rpm. The ignition drop as less than 250 rpm and
both
> ignitions were the same. At full throttle I could not get more than 4400
> rpm and it ran rough again. Back at the hangar I tried a few diagnostic
> things. With the electric fuel pump on I see about 2.5-2.9 psi. With the
> engine running and the electric pump off the fuel pressure drops to~0.5
> psi. I took the fuel pump off the engine and operated it by hand, it
seems
> OK but needs the electric pump on to keep it primed. The throw of the
pump
> plunger is ~3/8"-7/16". Checking the pump cam with a rod and measuring
the
> amount of difference from high cam to low cam it is barely 3/16" which
> seems very little. There is no sign of wear on the cam when looking at it
> through the pump mounting hole. I had thought that the pump filter was
> contaminated but the pump, when off the engine, seems OK.
> The questions:
> 1) Is this a normal throw for this cam?
> 2) Why does it need so much choke when it did not do so before all the
> fuel problems.
> 3) Is there something else I am missing that would cause these symptoms?
> Since pulling off the fuel pump off another mechanic remarked that the
> engine seemed very stiff to pull over with the prop, it had always been
> that way since new and I had attributed it to the engine gearbox
> combination. I removed the top plugs and the gearbox and the engine and
the
> gearbox are each quite smooth but not when the gearbox is mounted back on
> the engine. It feels like the plugs are still in and there is compression
> pressure causing resistance?
> I apologize for the long description.
> Henry
>
>

I have been working with gas tank sealants for over 20 years. I do not
know what form of PRO SEAL you used, what type did you use, the 890 or the
1440? But, I can tell you that ALL the gas tank sealants available in the
USA will NOT work with AutoGas (MoGas) that contains ethanol. The gas will
soften and cause leaks to the sealant. They are good, not great, with
MoGas that does NOT contain ethanol. YET! The 'Aromatics' in gas will
also attack tank sealants. Just not as fast as ethanol!
Also - Many, Many people put one layer of tank sealant over the top of the
old sealant... Ya CAN'T do that! The sealants DO NOT stick to them selves
once cured and especially after gas has been in the tank. You MUST remove
all the old sealant - Get down to bare metal - And start again.

As for your rotax running rough... Don't know... Maybe a broken part of
the sealant has blocked some orifice. I would fix one problem at a time.
Gas tank sure sounds like it should be first.

> I have a fuel problem that I would like your advice on. I have an RV-12
> with the Rotax 912ULS that only has about 75 hours on it over the last
> three or four years. I had some severe medical problems and my RV also
had
> some fuel problems. The fuel problems began with leakage from the tank. I
> built the tank as per Van's manual and it sat for about a year before I
put
> any fuel into it. It was then OK for well over two years before there
was a
> leak. It began as a minor leakage and I removed the tank and sealed, from
> the outside, one seam and a front corner. That did not stop the leak and
it
> got worse to the point that the tank lost about three gallons of auto
fuel
> over about four days. I removed the tank and could not find any sign of a
> leak with the tank on the bench even with fuel in the tank. I put the
tank
> back in and filled it, again with auto fuel. It was OK for about five
days
> and then began to leak again, this time it lost about ~five gallons and
> stripped the paint off the bottom of the plane, a real mess. I took a
sheet
> of newspaper and slid it under the tank, before I removed the fuel, and
> found that it was leaking at the rear right corner. When I took the tank
> out that time it did not leak on the bench until it had sat there for
over
> a week. The Pro-Seal softened up in places when it was wet with fuel but
it
> was OK when it dried out. While it was wet I could poke a Q-tip stick
> through the corner, the Pro-Seal was quite soft. had no ideas why the
> Pro-Seal broke down as it did but rather than risk another leak in
flight I
> made a new tank, this time without the side gauge and with a Moler
> mechanical gauge on the top. There was a lot of trouble starting the
engine
> and when it did start, with full choke and no throttle, it ran rough. I
had
> to run the engine on full choke for at least five minutes before I could
> even crack the throttle open. I cleaned both carbs and tried again.
Before
> the five minutes were up if I tried to open the throttle the engine would
> die. Once it had really warmed up it seemed OK. I did the pre-flight
check
> with a run up at 4000 rpm. The ignition drop as less than 250 rpm and
both
> ignitions were the same. At full throttle I could not get more than 4400
> rpm and it ran rough again. Back at the hangar I tried a few diagnostic
> things. With the electric fuel pump on I see about 2.5-2.9 psi. With the
> engine running and the electric pump off the fuel pressure drops to~0.5
> psi. I took the fuel pump off the engine and operated it by hand, it
seems
> OK but needs the electric pump on to keep it primed. The throw of the
pump
> plunger is ~3/8"-7/16". Checking the pump cam with a rod and measuring
the
> amount of difference from high cam to low cam it is barely 3/16" which
> seems very little. There is no sign of wear on the cam when looking at it
> through the pump mounting hole. I had thought that the pump filter was
> contaminated but the pump, when off the engine, seems OK.
> The questions:
> 1) Is this a normal throw for this cam?
> 2) Why does it need so much choke when it did not do so before all the
> fuel problems.
> 3) Is there something else I am missing that would cause these symptoms?
> Since pulling off the fuel pump off another mechanic remarked that the
> engine seemed very stiff to pull over with the prop, it had always been
> that way since new and I had attributed it to the engine gearbox
> combination. I removed the top plugs and the gearbox and the engine and
the
> gearbox are each quite smooth but not when the gearbox is mounted back on
> the engine. It feels like the plugs are still in and there is compression
> pressure causing resistance?
> I apologize for the long description.
> Henry
>
>

Matt Dralle
Matronics Email List Administrator
[ Note: This FAQ was designed to be displayed with a fixed width font such
as
Courier. Proportional fonts will cause display formatting
errors. ]
This FAQ can also be viewed in HTML online at the following address:

http://www.matronics.com/FAQ/RotaxEngines-List.htm ************************************************************
******* LIST POLICIES AND FREQUENTLY ASKED QUESTIONS *******
************************************************************
PLEASE READ. This document contains RotaxEngines-List policies and
information
for new and old subscribers. Understanding the RotaxEngines-List policies
will
minimize problems for the Administrator, and will help keep the
RotaxEngines-List
running smoothly for all of us.
******************************************
*** Quick Start Guide to List Features ***
******************************************

There are many features available on the Matronics Email Lists and each
one is described in detailed below. However, using the List Navigator
you can quickly access the complete set of features available for this
List. The List Navigator can be found at the following URL:

Simply go to the Web Page shown below and enter your email address and
select the List(s) that you wish to subscribe or unsubscribed from. You
may also use the handy "Find" function to determine the exact syntax of
your email address as it is subscribed to the List. Please see the
complete instructions at the top of the Web Page for more information.
The Subscribe/Unsubscribe web page is:

Note that you will receive TWO conformation emails regarding your
subsciption
process. The first verifies that your subscription/unsubsciption
request
was received, and the second confirms that the process has been
completed.

You should receive the first email within a few minutes of your request.
The second conformation will arrive in less than 24 hours. You cannot
post

until you receive the second conformation email message.
*****************************
*** How to Post a Message ***
*****************************

Your message will be redistributed to everyone currently subscribed
to the List.
*****************************************************
*** SPAM Fighter - You Must be Subscribed to Post ***
*****************************************************

When a new post is received by the system, the From: line of the message
is checked and compared against the current subscription list. If the
email address is found, the message is passed on to the List Processor

- The Matronics RotaxEngines-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot vote in polls in this forumYou cannot attach files in this forumYou can download files in this forum